1. Technical Field
The present invention relates to a thermal analyzer for measuring a physical change of a sample along with its temperature change caused by heating the sample.
2. Description of the Related Art
Conventionally, as a technique of evaluating temperature characteristics of a sample, there has been employed a technique called thermal analysis for measuring a physical change of a sample along with its temperature change caused by heating the sample. A definition of thermal analysis can be found in JIS K 0129: 2005 “General rules for thermal analysis,” and thermal analysis, according to this definition, includes all techniques that measure the physical properties of a measurement target (sample) under program controlled temperatures. Five common thermal analysis methods are (1) Differential Thermal Analysis (DTA) that detects temperatures (temperature difference), (2) Differential Scanning Calorimetry (DSC) that detects a heat flow difference, (3) Thermogravimetry (TG) that detects masses (weight change), (4) Thermomechanical Analysis (TMA) and (5) Dynamic Mechanical Analysis (DMA) that detect mechanical properties.
The thermal analyzer 1000 shown in FIG. 9 represents a known example of thermal analyzers. The thermal analyzer 1000 performs Thermogravimetry (TG), and, as required, Differential Thermal Analysis (DTA). This thermal analyzer is provided with: a cylindrical furnace tube 9 having an outlet 9b which is reduced in diameter and is arranged at an anterior end portion 9a; a cylindrical heating furnace 3 surrounding the furnace tube 9 from outside; sample holders 41 and 42 arranged inside the furnace tube 9 and holding samples S1 and S2, respectively, via sample containers; a measurement chamber 30 connected air tight to a posterior end portion 9d of the furnace tube 9; and a weight detector 32 arranged inside a measurement chamber 30 to measure weight changes of samples (cf. JP-A-11-326249, JP-A-2007-232479, and JP-A-7-146262). The thermal analyzer also includes two supporting pillars 218 extending downward from the lower end of the heating furnace 3. The supporting pillars 218 are connected to a support base 200. A flange 7 is fixed to the outer side of the posterior end portion 9d of the furnace tube 9, and a supporting pillar 216 extends downward from the lower end of the flange 7. The supporting pillar 216 is also connected to the support base 200. The support base 200 and the measurement chamber 30 are mounted on a base 10. The support base 200 can be moved back and forth with a linear actuator 220 along the axial direction O of the furnace tube 9.
The heating furnace 3 heats the sample holders 41 and 42 from outside of the furnace tube 9, and the weight detector 32 detects the weights of the samples S1 and S2 as they change with temperature.
Referring to FIG. 10, the linear actuator 220 moves the support base 200 toward the anterior side of the furnace tube 9 (leftward in FIG. 10) when setting samples S1 and S2 to the sample holders 41 and 42 or when replacing samples S1 and S2, together with the heating furnace 3 and the furnace tube 9 fixed to the support base 200. This exposes the sample holders 41 and 42 on the posterior side of the furnace tube 9, enabling setting or replacing the samples S1 and S2.
While the foregoing thermal analyzer can be used to detect the required thermophysical properties, changes in the sample being studied by thermal analysis cannot be visually observed. This is because the furnace tube 9 is typically formed of a ceramic such as sintered alumina, or a heat resistant metal such as Inconel (registered trademark), and is covered with the heating furnace 3.
With respect to these conventional thermal analyzers, the Applicants of the present application have proposed, in JP-A-2013-185834, a new thermal analyzer that includes a furnace tube formed of a transparent material, and in which the furnace tube is exposed by moving forward only the heating furnace for sample observation so that a sample can be observed from outside of the exposed furnace tube. It is also proposed in JP-A-2013-185834 to cover a part of the exposed furnace tube with a heat conducting member, and partially inserting the heat conducting member into the heating furnace to transfer the heat of the heating furnace to the exposed furnace tube, and maintain the sample in a heated state at the sample observation position.
A thermal analysis using the technique in JP-A-2013-185834 enables a sample observation at temperatures as high as 500° C. when the technique is adapted to indirectly heat the sample inside the exposed furnace tube with the heat conducting member. However, such indirect heating with the heat conducting member may not be sufficient to meet the requirement for observing a sample at high temperatures above 500° C. in a thermal analysis.
When performing the Thermogravimetry/Differential Thermal Analysis (TG/DTA) as shown in FIG. 9, the measurement sample S1 is covered with the heating furnace 3. For this reason, as shown in FIG. 6, the radiation heat RH from the heating furnace 3 directly radiates onto the measurement sample S1 inside the sample container 51. DTA obtains a differential heat signal resulting from the melting, decomposition, or other changes of the measurement sample S1. However, the amount of the radiation heat RH absorbed by the measurement sample S1 changes when changes occur in sample color, or when the measurement sample S1 melts and changes its shape under heat. Such changes in radiation heat are reflected in the differential heat signal, and the measurement accuracy suffers.